Cell adhesion is a complex process that is important for maintaining tissue integrity and generating physical and permeability barriers within the body. All tissues are divided into discrete compartments, each of which is composed of a specific cell type that adheres to similar cell types. Such adhesion triggers the formation of intercellular junctions (i.e., readily definable contact sites on the surfaces of adjacent cells that are adhering to one another), also known as tight junctions, gap junctions and belt desmosomes. The formation of such junctions gives rise to physical and permeability barriers that restrict the free passage of cells and other biological substances from one tissue compartment to another. For example, the blood vessels of all tissues are composed of endothelial cells. In order for components in the blood to enter a given tissue compartment, they must first pass from the lumen of a blood vessel through the barrier formed by the endothelial cells of that vessel. Similarly, in order for substances to enter the body via the gut, the substances must first pass through a barrier formed by the epithelial cells of that tissue. To enter the blood via the skin, both epithelial and endothelial cell layers must be crossed.
Cell adhesion is mediated by specific cell surface adhesion molecules (CAMs). There are many different families of CAMs, including the immunoglobulin, integrin, selectin and cadherin superfamilies, and each cell type expresses a unique combination of these molecules. Cadherins are a rapidly expanding family of calcium-dependent CAMs (Munro et al., In: Cell Adhesion and Invasion in Cancer Metastasis, P. Brodt, ed., pp. 17–34, RG Landes Co. (Austin Tex., 1996). The classical cadherins (abbreviated CADs) are integral membrane glycoproteins that generally promote cell adhesion through homophilic interactions (a CAD on the surface of one cell binds to an identical CAD on the surface of another cell), although CADs also appear to be capable of forming heterotypic complexes under certain circumstances and with lower affinity. Cadherins have been shown to regulate epithelial, endothelial, neural and cancer cell adhesion, and different CADs are expressed on different cell types. N (neural)—cadherin is predominantly expressed by neural cells, endothelial cells and a variety of cancer cell types. E (epithelial)—cadherin is predominantly expressed by epithelial cells. Other illustrative CADs include P (placental)—cadherin, which is found in human skin and R (retinal)—cadherin. A detailed discussion of the classical cadherins is provided in Munro S B et al., 1996, In: Cell Adhesion and Invasion in Cancer Metastasis, P. Brodt, ed., pp. 17–34 (RG Landes Company, Austin Tex.).
The structures of the CADs are generally similar. As illustrated in FIG. 1, CADs are composed of five extracellular domains (EC1–EC5), a single hydrophobic domain (TM) that transverses the plasma membrane (PM), and two cytoplasmic domains (CP1 and CP2). The calcium binding motifs DXNDN (SEQ ID NO:8), DXD and LDRE (SEQ ID NO:9) are interspersed throughout the extracellular domains. The first extracellular domain (EC1) contains the classical cadherin cell adhesion recognition (CAR) sequence, HAV (His-Ala-Val), along with flanking sequences on either side of the CAR sequence that may play a role in conferring specificity. Synthetic peptides containing the CAR sequence and antibodies directed against the CAR sequence have been shown to inhibit CAD-dependent processes (Munro et al., supra; Blaschuk et al., J. Mol. Biol. 211:679–82, 1990; Blaschuk et al., Develop. Biol. 139:227–29, 1990; Alexander et al., J. Cell. Physiol. 156:610–18, 1993). The three-dimensional solution and crystal structures of the EC1 domain have been determined (Overduin et al., Science 267:386–389, 1995; Shapiro et al., Nature 374:327–337, 1995).
Although cell adhesion is required for certain normal physiological functions, there are situations in which cell adhesion is undesirable. For example, many pathologies (such as cancer, autoimmune and inflammatory diseases) involve abnormal cellular adhesion and/or migration. Cell adhesion may also play a role in graft rejection. In such circumstances, modulation of cell adhesion may be desirable.
Cancer is a significant health problem throughout the world. Although advances have been made in detection and therapy of cancer, no universally successful method for the prevention or treatment of human cancer is currently available. For example, among women, breast and ovarian cancer are prevalent in the United States and other countries. Breast cancer, in particular, remains the second leading cause of cancer-related deaths in women, affecting more than 180,000 women in the United States each year. For women in North America, the life-time odds of getting breast cancer are now one in eight. Management of the disease currently relies on a combination of early diagnosis (through routine breast screening procedures) and aggressive treatment, which may include one or more of a variety of treatments such as surgery, radiotherapy, chemotherapy and hormone therapy.
Prostate cancer is the most common form of cancer among males, with an estimated incidence of 30% in men over the age of 50. Human prostate cancer has the propensity to metastasize to bone. Treatment is commonly based on surgery and/or radiation therapy, but these methods are ineffective in a significant percentage of cases, and this prevalent disease is currently the second leading cause of cancer death among men in the U.S.
Cell adhesion is a complex process that is important for tumor growth. Interactions between cell adhesion molecules, such as classical cadherins, are responsible for binding of tumor cells to one another, as well as for angiogenesis (i.e., the growth of blood vessels from pre-existing blood vessels). Many cancerous tumors are solid masses of cells which require nourishment via blood vessels, and the formation of new capillaries is a prerequisite for tumor growth and the emergence of metastases. Inhibition of undesirable cell adhesion mediated by classical cadherins provides promising new approaches for cancer therapy.
Accordingly, there is a need in the art for improved cancer therapeutic agents that inhibit tumor growth and/or metastasis by either modulating adhesion of cancer cells, or modulating the adhesion between the endothelial cells of both newly formed and pre-existing tumor blood vessels. There is also a need in the art for compounds that induce apoptosis in cancer cells. The present invention fulfills these needs and further provides other related advantages.
Nerve growth is promoted by a wide range of molecules, including the cell surface adhesion molecules (CAMs) NCAM and N-cadherin. In particular, N-cadherin is the predominant mediator of calcium-dependent adhesion in the nervous system. N-cadherin is known to promote neurite outgrowth via a homophilic binding mechanism. N-cadherin is normally found on both the advancing growth cone and on cellular substrates, and the inhibition of N-cadherin function results in diminished neurite outgrowth. Such inhibition may be the result of pathology or injury involving severed neuronal connections and/or spinal cord damage. In such cases, enhancement of N-cadherin mediated neurite outgrowth would be beneficial. However, previous attempts to promote neurite outgrowth have achieved limited success due, in part, to difficulties associated with maintaining continuous growth over a particular defined region.
Accordingly, there is a need in the art for compounds that modulate neural cell adhesion, migration and/or survival, such as compounds that direct neurite outgrowth, without the above-mentioned disadvantages. The present invention fulfills this need and further provides other related advantages.
In addition, permeability barriers arising from cell adhesion create difficulties for the delivery of drugs to specific tissues and tumors within the body. For example, skin patches are a convenient tool for administering drugs through the skin. However, the use of skin patches has been limited to small, hydrophobic molecules because of the epithelial and endothelial cell barriers. Similarly, endothelial cells render the blood capillaries largely impermeable to drugs, and the blood/brain barrier has hampered the targeting of drugs to the central nervous system. In addition, many solid tumors develop internal barriers that limit the delivery of anti-tumor drugs and antibodies to inner cells.
Attempts to facilitate the passage of drugs across such barriers generally rely on specific receptors or carrier proteins that transport molecules across barriers in vivo. However, such methods are often inefficient, due to low endogenous transport rates or to the poor functioning of a carrier protein with drugs. While improved efficiency has been achieved using a variety of chemical agents that disrupt cell adhesion, such agents are typically associated with undesirable side-effects, may require invasive procedures for administration and may result in irreversible effects. It has been suggested that linear synthetic peptides containing a cadherin CAR sequence may be employed for drug transport (WO 91/04745), but such peptides are often metabolically unstable and are generally considered to be poor therapeutic agents.
Accordingly, there is a need in the art for compounds that modulate cell adhesion and improve drug delivery across permeability barriers without such disadvantages. The present invention fulfills this need and further provides other related advantages.
Percutaneous transluminal coronary angioplasty (PTCA) is widely used as the primary treatment modality in many patients with coronary artery disease. PTCA can relieve myocardial ischemia in patients with coronary artery disease by reducing lumen obstruction and improving coronary flow. The use of this surgical procedure has grown rapidly. However, stenosis following PTCA remains a serious problem. In addition, stents are deployed in a large proportion of vascular interventions (˜70–90%) and the injury to the vessel wall from a stent can be a stimulus for restenosis. Restenosis results in significant morbidity and mortality and frequently necessitates further interventions such as repeat angioplasty or coronary bypass surgery. No surgical intervention or post-surgical treatment has proven universally effective in preventing restenosis. The processes responsible for restenosis are not completely understood but may result from a complex interplay among several different biologic agents and pathways, including overgrowth of smooth muscle cells in the intimal layers of the vessel.
Accordingly, there is a need in the art for compounds that modulate, and preferably inhibit, smooth muscle cell adhesion, proliferation, migration and/or survival. The present invention fulfills this need and further provides other related advantages.